The tonne (/tʌn/ ( listen)) (Non-SI unit, symbol: t),
commonly referred to as the metric ton in the United States, is a
non-SI metric unit of mass equal to 1,000 kilograms;[1][2][3][4]
or one megagram (Mg); it is equivalent to approximately 2,204.6
pounds,[5] 1.102 short tons (US) or 0.984 long tons (imperial).
Although not part of the SI, the tonne is accepted for use with SI
units and prefixes by the International Committee for Weights and
Measures.[6]

Symbol and abbreviations[edit]
The SI symbol for the tonne is "t", adopted at the same time as the
unit in 1879.[2] Its use is also official for the metric ton in the
United States, having been adopted by the United States National
Institute of Standards and Technology.[7] It is a symbol, not an
abbreviation, and should not be followed by a period. Informal and
non-approved symbols or abbreviations include "T", "mT", "MT", and
"mt".[8] Some of these are SI symbols for other units: "T" is the SI
symbol for the tesla and "Mt" is the SI symbol for megatonne
(equivalent to one teragram); if describing
TNT equivalentTNT equivalent units of
energy, this is equivalent to 4.184 petajoules.
Origin and spelling[edit]
In French and all English-speaking countries that are predominantly
metric, tonne is the correct spelling. It is usually pronounced the
same as ton /tʌn/, but when it is important to clarify that the
metric term is meant, rather than short ton, the final "e" can also be
pronounced, i.e. "tonny" /ˈtʌnɪ/.[9] In Australia, it is also
pronounced /tɒn/.[10]
Before metrication in the UK the unit used for most purposes was the
Imperial ton of 2,240 pounds avoirdupois (usually referred to as
the long ton in the US), equivalent to 1,016 kg, differing by
just 1.6% from the tonne. The UK Weights and Measures Act 1985
explicitly excluded from use for trade certain imperial units,
including the ton, unless the item being sold or the weighing
equipment being used was weighed or certified prior to 1 December
1980, and even then only if the buyer was made aware that the weight
of the item was measured in imperial units.[11][full citation
needed][12][13]
In the United States metric ton is the name for this unit used and
recommended by NIST;[7] an unqualified mention of a ton almost
invariably refers to a short ton of 2,000 pounds (907 kg), and
tonne is rarely used in speech or writing.
TonTon and tonne are both derived from a Germanic word in general use in
the
North SeaNorth Sea area since the
Middle AgesMiddle Ages (cf.
Old EnglishOld English and Old
Frisian tunne,
Old High GermanOld High German and
Medieval LatinMedieval Latin tunna, German and
French tonne) to designate a large cask, or tun.[14] A full tun,
standing about a metre high, could easily weigh a tonne. An English
tun (an old wine cask volume measurement equivalent to 954 litres) of
wine weighs roughly a tonne, 954 kg if full of water, a little
less for wine.
The spelling tonne pre-dates the introduction of the SI in 1960; it
has been used with this meaning in France since 1842,[15] when there
were no metric prefixes for multiples of 106 and above, and is now
used as the standard spelling for the metric mass measurement in most
English-speaking countries.[16][17][18][19] In the United States, the
unit was originally referred to using the French words millier or
tonneau,[20] but these terms are now obsolete.[3] The Imperial and US
customary units comparable to the tonne are both spelled ton in
English, though they differ in mass.
Conversions[edit]
One tonne is equivalent to:

Derived units[edit]
For multiples of the tonne, it is more usual to speak of thousands or
millions of tonnes. Kilotonne, megatonne, and gigatonne are more
usually used for the energy of nuclear explosions and other events,
often loosely as approximate figures. When used in this context, there
is little need to distinguish between metric and other tons, and the
unit is spelt either as ton or tonne with the relevant prefix
attached.[23]

*The equivalent units columns use the short scale large-number naming
system currently used in most English-language countries, e.g. 1
billion = 1,000 million = 1,000,000,000.
†Values in the equivalent short and long tons columns are rounded to
five significant figures, see Conversions for exact values.
ǂThough non-standard, the symbol "kt" is also used for knot, a unit
of speed for aircraft and sea-going vessels, and should not be
confused with kilotonne.
Alternative usage[edit]
A metric ton unit (MTU) can mean 10 kilograms (22 lb) within
metal (e.g. tungsten, manganese) trading, particularly within the US.
It traditionally referred to a metric ton of ore containing 1% (i.e.
10 kg) of metal.[24][25]
In the case of uranium, the acronym MTU is sometimes considered to be
metric ton of uranium, meaning 1,000 kg.[26][27][28][29]
A gigatonne of carbon dioxide equivalent (GtCO2eq) is a unit used by
the UN climate change panel, IPCC, to measure the effect of a
technology or process on global warming.
Use of mass as proxy for energy[edit]
Main article: TNT equivalent
The tonne of trinitrotoluene (TNT) is used as a proxy for energy,
usually of explosions (TNT is a common high explosive). Prefixes are
used: kiloton(ne), megaton(ne), gigaton(ne), especially for expressing
nuclear weapon yield, based on a specific combustion energy of TNT of
about 4.2 MJ/kg (or one thermochemical calorie per milligram).
Hence, 1 t TNT = 4.2 GJ, 1 kt TNT = 4.2 TJ, 1 Mt TNT =
4.2 PJ.
The SI unit of energy is the joule. Assuming that a TNT explosion
releases 1,000 small (thermochemical) calories per gram
(4.2 kJ/g), one tonne of TNT is equivalent to 4.2 gigajoules.
In the petroleum industry the tonne of oil equivalent (toe) is a unit
of energy: the amount of energy released by burning one tonne of crude
oil, approximately 42 GJ. There are several slightly different
definitions. This is ten times as much as a tonne of TNT because
atmospheric oxygen is used.
Unit of force[edit]
Like the gram and the kilogram, the tonne gave rise to a (now
obsolete) force unit of the same name, the tonne-force, equivalent to
about 9.8 kilonewtons: a unit also often called simply "tonne" or
"metric ton" without identifying it as a unit of force. In contrast to
the tonne as a mass unit, the tonne-force or metric ton-force is not
acceptable for use with SI, partly because it is not an exact multiple
of the SI unit of force, the newton.
See also[edit]